test(client): cover TTL and pending expiry without poll coupling

crates/irtt-client/tests/linux_transport.rs

@@ -14,6 +14,8 @@ use irtt_proto::{decode_request, Clock, DecodedRequestKind, ReceivedStats, Stamp
 use irtt_server::{ServerConfig, ServerCore};
 use nix::sys::socket::{recvmsg, ControlMessageOwned, MsgFlags};
 
+const TEST_TTL: u32 = 37;
+
 // A compliant packet peer uses the real server core. Its receive-side IP_TOS
 // observation is independent of the client/server parameter agreement.
 fn peer(dscp_allowed: bool, probes: usize) -> (SocketAddr, thread::JoinHandle<Vec<u8>>) {
@@ -24,6 +26,7 @@ fn peer(dscp_allowed: bool, probes: usize) -> (SocketAddr, thread::JoinHandle<Ve
     socket2::SockRef::from(&socket)
         .set_recv_tos_v4(true)
         .unwrap();
+    nix::sys::socket::setsockopt(&socket, nix::sys::socket::sockopt::Ipv4RecvTtl, &true).unwrap();
     let addr = socket.local_addr().unwrap();
     let task = thread::spawn(move || {
         let mut core = ServerCore::new(
@@ -35,7 +38,7 @@ fn peer(dscp_allowed: bool, probes: usize) -> (SocketAddr, thread::JoinHandle<Ve
         // OPEN, every ECHO, then CLOSE.
         for _ in 0..probes + 2 {
             let mut bytes = [0; 2048];
-            let mut control = nix::cmsg_space!(u8);
+            let mut control = nix::cmsg_space!(u8, i32);
             let mut iov = [IoSliceMut::new(&mut bytes)];
             let msg = recvmsg::<nix::sys::socket::SockaddrIn>(
                 std::os::fd::AsRawFd::as_raw_fd(&socket),
@@ -54,6 +57,18 @@ fn peer(dscp_allowed: bool, probes: usize) -> (SocketAddr, thread::JoinHandle<Ve
                     _ => None,
                 })
                 .expect("Linux must report IP_TOS");
+            let ttl = msg
+                .cmsgs()
+                .unwrap()
+                .find_map(|message| match message {
+                    ControlMessageOwned::Ipv4Ttl(ttl) => Some(ttl),
+                    _ => None,
+                })
+                .expect("Linux must report IP_TTL");
+            assert_eq!(
+                ttl, TEST_TTL as i32,
+                "configured TTL must survive OPEN, ECHO and CLOSE"
+            );
             markings.push(marking);
             let source = SocketAddr::from((source.ip(), source.port()));
             if let Some(reply) = core.handle_datagram(source, &bytes[..size]).unwrap() {
@@ -79,6 +94,7 @@ fn config(addr: SocketAddr) -> ClientConfig {
         length: 128,
         open_timeouts: vec![Duration::from_secs(1)],
         socket_config: SocketConfig {
+            ttl: Some(TEST_TTL),
             recv_timeout: Some(Duration::from_secs(1)),
             ..SocketConfig::default()
         },